Further studies on the renin-angiotensin system are under investigation. In particular, the levels of inactive renin will be studied in a variety of conditions and also the various factors which convert inactive to active renin. Preliminary studies suggest that prostaglandins may be involved since indomethacin administration to humans lowers active but not inactive renin. Both human and an in vitro model will be used to study this problem. Since several lines of evidence suggest an unknown factor may regulate aldosterone secretion, we have set up the in vitro rat glomerulosa cell assay to search for such a compound in human urine. Our initial aim is to confirm the published report, and if confirmed, to study the physiological factors which control the excretion of this compound.